An image reading apparatus comprises a reading unit including a movable sensor, a first reading mechanism which moves the reading unit to read an original placed on a platen, a second reading mechanism which conveys the original relative to the reading unit to read the original, a common driving source which drives the first reading mechanism and the second reading mechanism, a transfer unit which transfers a driving force from the driving source to the first reading mechanism and the second reading mechanism, and a switching unit which switches rotation used to drive the second reading mechanism to one of forward rotation and reverse rotation with respect to rotation of the driving source in one direction, the switching unit operating as the reading unit moves.